Vulcanization composition for unsaturated polymers

ABSTRACT

The present invention relates to the field of the vulcanization of unsaturated polymers, in particular unsaturated halogenated polymers and more particularly unsaturated chlorinated polymers, such as, for example, polychloroprene, by using, as vulcanization agent, a mixture of bis(2,5-dimercapto-1,3,4-thiadiazole) and at least one organic base. The present invention relates to the process for the vulcanization of the said polymers with the said vulcanization mixture.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase application of PCTInternational Application No. PCT/FR2012/051249, filed Jun. 6, 2012, andclaims priority to French Patent Application No. 1154904, filed Jun. 6,2011, the disclosures of which are incorporated by reference in theirentirety for all purposes.

FIELD OF THE INVENTION

The present invention relates to the field of the vulcanization ofunsaturated polymers, in particular unsaturated halogenated polymers,more particularly unsaturated chlorinated polymers, such as, forexample, polychloroprene. The present invention relates in particular tothe vulcanization agents which are employed in these processes asvulcanization accelerators.

BACKGROUND OF THE INVENTION

The accelerators used in the vulcanization of unsaturated polymers,polyolefins or rubbers, in particular halogenated rubbers, such aspolychloroprene, are generally thiourea-based accelerators which todaycompose the crosslinking systems for rubbers having the bestperformance.

Ethylene thiourea (ETU) is the reference thiourea used today for thevulcanization of chlorinated rubbers, in particular polychloroprene.However, ETU is toxic in itself, classified in carcinogenic group 2,according to the classification of the European Union, the IARC(International Agency for Research on Cancer) and the EPA (EnvironmentalProtection Agency).

It is consequently necessary to henceforth look for replacement productswhich are less toxic, which are more environmentally friendly and whichexhibit an effectiveness at least as good as that of thiourea-basedaccelerators, in particular ETU, in vulcanization processes.

The literature already provides some examples of vulcanization agents orvulcanization accelerators other than thiourea derivatives. For example,Patent U.S. Pat. No. 4,288,576 describes the use of2,5-dimercapto-1,3,4-thiadiazole for the vulcanization of saturatedchlorinated polymers, in the presence of a basic compound chosen fromamines, amine salts, quaternary ammonium salts, aromatic guanidines andthe condensation products of aniline with an aldehyde.

As other examples, Patent U.S. Pat. No. 5,391,621 describes the use ofcertain organopolysulphide compounds derived from 1,3,4-thiadiazole asagents for the vulcanization of chlorinated polymers. Otherpolysulphides, poly[2,5-bis(polysulphano)-1,3,4-thiadiazoles], aredescribed in

Patent U.S. Pat. No. 5,563,240, where they are of use as agents for thevulcanization of polychloroprene.

Patent Application EP 0 796 890 describes the vulcanization ofhalogenated acrylic rubbers in the presence of2,5-dimercapto-1,3,4-thiadiazole or derivatives and of a metaldialkyldithiocarbamate.

More recently, Patent Application US 2003/153652 also presentscompositions for vulcanizing chlorinated polymers, the said compositionsresulting from the mixing of a zeolite compound with a vulcanizationagent chosen from mercaptotriazines, thiadiazoles and thiurams.

The publication “An improved curing system for chlorine-containingpolymers”, by R. F. Ohm and T. C. Taylor (which appeared in “RubberWorld”, March 1997, pages 33 to 38), presents a comparative studybetween ETU and DMTD (2,5-dimercapto-1,3,4-thiadiazole), which are usedas agents for the vulcanization of polychloroprene in combination withvulcanization activators.

Despite these solutions already put forward for the replacement of ETU,a need remains, however, for vulcanization compositions which are evenmore effective, in particular for the vulcanization of unsaturatedpolymers, especially of unsaturated halogenated polymers and moreparticularly of unsaturated chlorinated polymers, more environmentallyfriendly and capable of conferring, on the vulcanized polymers,mechanical properties and properties of resistance to ageing which arefurther improved.

SUMMARY OF THE INVENTION

A first objective of the present invention consists in providing anagent (or accelerator) for the vulcanization of unsaturated polymers, inparticular of polyalkadienes, more particularly of unsaturatedhalogenated polymers, typically of unsaturated chlorinated polymers andin particular polychloroprene, the said agent or acceleratoradvantageously having to be nontoxic or only very slightly toxic andmore environmentally friendly.

Another objective of the present invention consists in providing avulcanization accelerator which is less toxic than ETU and in particularwhich does not release compounds of nitrosamine type.

Yet another objective consists in providing a vulcanization agent whichconfers, on the unsaturated polymers, in particular unsaturatedhalogenated polymers, for example unsaturated chlorinated polymers, inparticular of polychloroprene type, mechanical properties equivalent tothose obtained with systems employing toxic accelerators.

As another objective of the present invention, the vulcanization agentprovided can confer good ageing properties on the polymers. In addition,an objective also consists in providing a vulcanization acceleratorwhich makes it possible to increase the scorch time (or prevulcanizationtime).

Yet another objective consists in reducing the amount of inorganicvulcanization agents, generally metal oxides, in particular zinc and/ormagnesium oxides, used in the vulcanization of unsaturated polymers, inparticular unsaturated halogenated polymers, more specificallyunsaturated chlorinated polymers, without affecting the mechanical,rheological and other properties thereof, thus making it possible toalso reduce the amount of toxic effluents associated with the process,while also reducing the production costs.

The Applicant Company has now discovered that the abovementionedobjectives can be achieved in all, or at least in part, by virtue of theuse of the vulcanization accelerator which is a subject-matter of theinvention which will be described in detail below.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph of the change in torque as a function of time formixtures containing vulcanization formulations.

DETAILED DESCRIPTION OF THE INVENTION

According to a first aspect, the invention relates to the use, as agentfor the vulcanization of unsaturated polymers, in particular unsaturatedhalogenated polymers, more particularly unsaturated chlorinatedpolymers, of at least one mixture comprisingbis(2,5-dimercapto-1,3,4-thiadiazole), denoted bis-DMTD in thecontinuation of the present description, and at least one organic base.

bis-DMTD corresponds to one of the two following structures, dependingon the tautomeric forms selected:

The process for the manufacture of bis-DMTD has been known for manyyears and is, for example, described in Patent ApplicationCN-A-101096366. A process for the preparation of bis-DMTD which is evenmore environmentally friendly has recently been described in PatentApplication EP-A-2 272 836.

bis-DMTD is today mainly used in lubricant compositions but is used to avery slight extent in compositions comprising natural, artificial orsynthetic rubbers, where it generally acts as preservative and has neverbeen described as such as an additive for the vulcanization ofunsaturated polymers. bis-DMTD does not generate nitrosamines.

The organic base used in combination (mixture) with the bis-DMTD can beof any type known to a person skilled in the art. However, preference isgiven to nitrogenous organic bases and more particularly guanidines,which are optionally substituted, with which an entirely unexpectedeffect of improving the kinetics of vulcanization and the scorch timehas been observed, when they are used in combination with bis-DMTD.

Entirely noteworthy results have been obtained with guanidinessubstituted by one or more aryl groups, preferably by one or two arylgroups, preferably by two aryl groups. An organic base which isaltogether preferred in the context of the present invention isdiphenylguanidine.

As a general rule, the bis-DMTD/organic amine molar ratio is between1:99 and 99:1, preferably between 25:75 and 75:25, for exampleapproximately 50:50.

According to an alternative form of the invention, preference is givento a vulcanization composition in which the bis-DMTD/organic amine molarratio is between 40:60 and 99:1, preferably between 50:50 and 99:1, morepreferably between 60:40 and 99:1, entirely preferably between 70:30 and99:1.

The polymers which can advantageously be vulcanized by virtue of theabovementioned mixture are unsaturated polymers, in particularunsaturated halogenated polymers, more particularly unsaturatedchlorinated polymers. More specifically, the polymers targeted in thepresent invention are all the polymers and copolymers comprising atleast one ethylenic unsaturation, among which may be mentioned, asnonlimiting examples, natural, artificial or synthetic rubbers,poly(butadienes), styrene and butadiene copolymers (SBRs), acrylonitrileand butadiene copolymers (NBRs), ethylene/propylene/diene copolymers(EPDMs), butyl rubbers, SBSs, halogenated polyalkadienes, in particularchlorinated polyalkadienes, and others, as well as the mixtures of thesehomopolymers and copolymers in all proportions.

According to a preferred aspect, the chlorinated polyalkadienes comprisemore than 1% by weight of chlorine, preferably more than 2% by weight ofchlorine and more preferably approximately 5% by weight of chlorine. Thechlorine content can reach up to 40% by weight of chlorine, with respectto the total weight of the polymer.

Mention may be made, as examples of such chlorinated polyalkadienes,without implied limitation, of chloroprene rubbers or polychloroprenes,chlorinated natural rubbers, chlorinated polyolefins, chlorinated butylrubbers and others.

According to one embodiment of the present invention, preference is veryparticularly given to the use of the abovementioned vulcanizationmixture for the vulcanization of polychloroprene, denoted CR in thecontinuation.

Such mixtures can comprise from 10% by weight to 90% by weight of eachof the polymers, preferably from 25% by weight to 75% by weight, withrespect to the total weight of the polymers in the mixtures.

According to a preferred embodiment, the chlorinated polymers which canbe used in the context of the present invention are chlorinated polymerscomprising one or more ethylenic unsaturations and, entirely preferably,the chlorinated polymers targeted in the present invention arepolychloroprenes, alone or as blends with other homopolymers and/orcopolymers, as indicated above.

The bis-DMTD, in combination with an organic base, in particular anitrogenous organic base, more particularly a guanidine, actssynergistically in the vulcanization of the unsaturated polymers.bis-DMTD appears to be a good sulphur donor, which makes it a goodvulcanization agent. The amine bases promote, on the one hand, therelease of the sulphur present in the bis-DMTD, which improves theproperties of the vulcanisate, and, on the other hand, they improve thekinetics of vulcanization, while maintaining a certain scorch safety.

According to another embodiment, sulphur can be added to thevulcanization process employing the vulcanizing composition according tothe present invention. This is because it has been discovered that theaddition of a small amount of sulphur to the bis-DMTD can catalyse thereaction and thus increase the bridging density. This makes it possibleto obtain a very high degree of crosslinking, which confers excellentcompression set properties and also very slight swellings in oil of thevulcanized polymer thus obtained.

According to yet another embodiment, the bis-DMTD can additionally beemployed on an elastomer support, in order to promote the dispersionthereof and thus to reduce the mixing times.

The use of bis-DMTD, in combination with at least one organic base, forexample a guanidine, as vulcanization accelerator has proved to beentirely effective during the vulcanization of polychloroprene. Inparticular, the kinetics of vulcanization employing a bis-DMTD/organicbase mixture have proven to be comparable, indeed even superior, to thekinetics of vulcanization observed in the presence of ETU.

In addition to rapid kinetics of vulcanization, the use of thebis-DMTD/organic base mixture in place of ETU as vulcanization agentmakes it possible to confer, on the unsaturated polymers, in particularunsaturated halogenated polymers, a good tear strength and a goodtensile strength, and also good resistance to ageing.

A decrease in the crystallization effect by an increase in the bridgingdegree has also been observed. This represents a considerable advantagewhen it is known that the crystallization is a very harmful phenomenonwell known to a person skilled in the art which brings about hardeningof the CR-base mixtures, which limits their lifetime.

As another advantage, it has likewise been observed that the scorch timeof the unsaturated polymers vulcanized by the bis-DMTD/organic basemixture can be effectively controlled by means of retardants appropriateto this novel vulcanization system (for example MBTS and/or CTPI inpolychloroprene).

According to an embodiment of the present invention, thebis-DMTD/organic base mixture is advantageously used as acceleratingagent for the vulcanization of chlorinated polymers, in combination withone or more inorganic vulcanization agents well known to a personskilled in the art. According to a preferred aspect, the inorganicvulcanization agents are chosen from metal oxides and in particular fromzinc oxide (ZnO), magnesium oxide (MgO) and others, and also themixtures of two or more of them in all proportions.

According to another aspect, the present invention relates to theprocess for the vulcanization of an unsaturated polymer, the saidprocess comprising at least the following stages:

-   mixing the said unsaturated polymer with the bis-DMTD/organic base    mixture, optionally sulphur and optionally one or more inorganic    vulcanization agents, as described above,-   vulcanizing the said unsaturated polymer, according to procedures    known to a person skilled in the art, and-   recovering the said vulcanized unsaturated polymer.

The mixing of the unsaturated polymer with the bis-DMTD/organic basecombination can be carried out according to any technique known per se,for example as a masterbatch (with regard to molten polymer, solidpolymer, as granules, as chips, and others) or in paste form (forexample with regard to wax or with a high oil content). The bis-DMTD andthe organic base can be added simultaneously or separately. As indicatedabove, the bis-DMTD can be introduced in the supported form, for examplesupported on an olefin, in order to reduce the mixing time of the saidbis-DMTD with the polymer to be vulcanized.

In order to carry out the vulcanization, as a function of the finalproperties required, sulphur can be added simultaneously or before orsubsequently to the bis-DMTD/organic base mixture and simultaneously orbefore or subsequently to the inorganic agents (in particular metaloxides). A person skilled in the art, familiar with the techniques andconditions for the vulcanization of unsaturated polymers, will know howto adapt the process of the invention as a function of the nature of thevulcanization agents and of the polymers which he wishes to vulcanize.

Thus, the vulcanization is carried out according to any procedure knownto a person skilled in the art, at a temperature, at a pressure and fora period of time which is appropriate according to the nature and thetype of vulcanization carried out.

Various additives can be added during the vulcanization processaccording to the present invention. These additives are well known to aperson skilled in the art and can be chosen, as nonlimiting examples,from lubricants, fillers, colourants, preservatives, antioxidants, heatstabilizers, UV stabilizers, vulcanization inhibitors or retardants,such as MBTS (mercaptobenzothiazole disulphide), CTPI(N-cyclohexylthiophthalimide), and others.

According to a preferred alternative form of the process of the presentinvention, the vulcanization can be carried out by simultaneously addinga mixture of the vulcanization agents, in or not in combination with thecovulcanization agents and other additives. Such a mixture (“mixture forvulcanization”) can thus comprise one or more of the followingingredients, which will be premetered according to the nature of thechlorinated polymer and the degree of vulcanization thereof desired:sulphur, bis-DMTD, organic base, inorganic agents and additive(s).

The present invention is now illustrated by means of the examples whichfollow and which do not have any limiting aim from the viewpoint of thescope of the present invention, which is defined by the appended claims.

EXAMPLES Example 1 Polychloroprene (CR) Vulcanization Test

All the mixtures are prepared in a 2.5 1 Repiquet internal mixer with astirring speed of 50 revolutions/min and a filling coefficient of 1.4.The CR base used exhibits the following composition (denoted “CR A base”in the continuation), in which the parts are expressed by weight:

CR A base - Materials Parts Neoprene WRT 100 N550 (carbon black) 50Kaolin grade B 20 DINP (phthalate oil) 20 Elastomag ® 170 (MgO) 4Stearin 0.5 Total 194.5

The mercaptan-grade neoprene WRT is generally vulcanized in the presenceof ETU, used as vulcanization accelerator, which confers the bestresults in terms of compression set (CS) and ageing. As indicated above,ETU is a toxic product due to its chemical nature and exhibits riskswhen used: ETU is regarded as carcinogenic by ingestion, mutagenic oralso as exhibiting risks of sterility by simple contact with the skin.

The present study shows that ETU can be advantageously replaced by thevulcanization mixture according to the invention. This study is carriedout using an appropriate 3×3 experimental plan. This experimental planmakes it possible to simultaneously vary three parameters over threelevels by using the symmetry conditions of a cube. For this plan, theworking hypotheses are as follows:

-   linear incrementation in the variables X1, X2 and X3;-   variation in the calculation values from −1 to +1 (methods);-   necessary changes in variables: experimental parameters towards the    calculation variables, for the interpretation of the results;-   no taking into account of the cross interactions: X1X2, X1X3, X2X3;-   no equidistances between the values;-   accuracy of 10 to 15%;-   second-degree equations.

This experimental plan makes it possible to obtain the change in theproperties with 9 mixtures instead of 27. The following parameters wereused:

-   X1: bis-DMTD: 0.5/0.75/1 (proportions by weight)-   X2: DPG: 0.1/0.2/0.3 (proportions by weight)-   X3: sulphur: 0/0.25/0.5 (proportions by weight)

The respective proportions by weight (parts by weight) of the variablesX1, X2 and X3 for the 9 tests (formulations F1 to F9) are collated inthe following Table 1, in which the bis-DMTD is in the powder form (soldby MLPC International), the DPG is Mixland®+DPG 80 GA F140 (sold by MLPCInternational), and the sulphur is Mixland®+SM300 80 GA F140 (sold byMLPC International):

TABLE 1 F1 F2 F3 F4 F5 F6 F7 F8 F9 bis-DMTD 0.5 0.75 1 1 0.5 0.75 0.75 10.5 DPG 0.1 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.3 Sulphur 0 0.25 0.5 0 0.250.5 0 0.25 0.5

These 9 formulations are used to prepare 9 mixtures M1 to M9respectively, with 194.5 parts by weight of the CR A base, 5 parts byweight of Mixland®+ZnO 90 GA F100 (zinc oxide, ZnO, sold by MLPCInternational), 1 part by weight of paraffin and 1 part by weight ofantioxidant Ekaland® 100, sold by MLPC International. A control mixture,denoted MO, devoid of sulphur, is similarly prepared with 194.5 parts byweight of the CR A base and 0.75 part by weight of ETU, instead of thebis-DMTD +DPG mixture.

The mixtures are prepared so as to obtain a blank weighing approximately600 g, corresponding to 2 plaques with a thickness of 2 mm, and theproduction of the CS graphs. Vulcanization is carried out to T₉₀(vulcanization time for obtaining 90% of the maximum torque) at 170° C.

The mixtures M1 to M9 and M0 are characterized mechanically (rheometricstudy). The change in the torque as a function of time, at a temperatureof 170° C., is shown in FIG. 1. It is noticed that the mixtures M2 to M9according to the invention exhibit a greater torque than that of thecontrol mixture M0, where the vulcanization agent used is ETU.

The mixtures M1 to M9 are characterized mechanically and the datacollected are used in the matrix of the experimental plan, which makesit possible to obtain a theoretical change in the properties of themixtures vulcanized with bis-DMTD. The experimental plan makes itpossible to obtain a change in 3D of the properties.

From this experimental plan, it can be accepted that DPG has asynergistic effect with the bis-DMTD, favouring the release of thesulphur atoms present in the bis-DMTD and thus improving the finalproperties of the material. It can also be deduced that the sulphur actsas catalyst of the reaction.

In conclusion, at the end of this experimental plan, two formulae can beselected as a function of the specifications to be achieved:

-   the mixture M7, which gives excellent results in ageing, better than    with the ETU-base control formula MO;-   an optimized mixture M10 (cf. Table 2), the composition of which was    deduced from the experimental plan and which gives better results    than with ETU at 70° C., in CS and in terms of swelling with oil.

TABLE 2 M0 M7 M10 CR A base 194.5 194.5 194.5 Ekaland ® + 100(antioxidant) 1 1 1 Paraffin 1 1 1 Mixland ® + ZnO 90 GA F100 5 5 5Mixland ® + ETU 80 GA F140 0.75 — — bis-DMTD powder (MLPC International)— 0.75 0.5 Mixland ® + SM300 80 GA F140 — 0.3 0.25 Mixland ® + DPG 80 GAF140 — — 0.2 Rheometry on an MDR at 170° C. - according to Standard NFT46-006 (or ISO 6502) C_(max)-C_(min) (dN · m) 14.1 14.6 — t_(s) 1 (min)1.1 0.82 — t_(c) 90 (min) 12.3 15.2 — Scorch time on a Mooney viscometerat 125° C. - according to Standard NFT 43-004 (or ISO 289-2) MS t3 9.256.1 — MS t10 13.3 10.5 — MS t18 24.3 14.8 — Dynamometric properties -according to Standard NFT 46-002 (or ISO 37) TS: Tensile strength (MPa)17 17 17.5 Eb: Elongation at break (%) 360 437 438 M100: Modulus at 100%(MPa) 3.9 3.9 3.8 M200: Modulus at 200% (MPa) 8.5 7.9 7.9 M300: Modulusat 300% (MPa) 14.1 12.2 12.6 Tearing (kN/m) according to Standard 41 4444 NFT 46-033 (or ISO 34-2) Shore A hardness according to 67 67 64Standard NFT 46-052 (or ISO 868) M0 M7 M10 Ageing, air, 72 hours, at100° C. - according to Standard NFT 46-004 (or ISO 188) TS (MPa) 16.8−1.4% 16.9 −0.7% 17.4 −1.0% Eb (%) 298 −17.3% 329 −24.6% 354 −19.1% M100(MPa) 5.3 36.3% 5.6 44.5% 5.5 43.3% M200 (MPa) 11.5 30.1% 10.9 37.9%10.7 36.5% M300 (MPa) — — 15.7 28.3% 15.5 23.8% Ageing, air, 7 days,100° C. - according to Standard NFT 46-004 (or ISO 188) TS (MPa) 17−0.1% 16.3 −3.9% — — Eb (%) 275 −23.5% 293 −32.8% — — M100 (MPa) 6.362.3% 6.3 61.6% — — M200 (MPa) 12.8 50.3% 12 52.0% — — Ageing, air, 10days, 100° C. - according to Standard NFT 46-004 (or ISO 188) TS (MPa)18 5.1% 16.4 −3.2% — — Eb (%) 273 −24.1% 291 −33.3% — — M100 (MPa) 7.285.0% 6.5 66.0% — — M200 (MPa) 13.7 61.0% 12.2 55.3% — — Ageing, air, 72hours, at 70° C. - according to Standard NFT 46-004 (or ISO 188) M0 M7M10 Swelling in oil (%) ISO R1817 39.3 40.6 32.8 CS at 25% (%)* 21.521.4 11.7 *according to standard NFT 46-011 (or ISO 815)

The coupling of bis-DMTD with an organic base (in this case, aguanidine, DPG), with or without the use of sulphur as catalyst, meetsthe environmental requirements by providing an unclassified system andnot producing nitrosamines, while guaranteeing, to the users, the finalproperties expected for a polychloroprene mixture.

In addition, this bis-DMTD/organic base (in the example, DPG) mixturemakes it possible to reduce the content of ZnO necessary, withoutaffecting the properties of the final product. In point of fact,reducing the metal oxides is one of the major ways of improving theenvironmental impact. The coupling provided in the present invention,due to the reduction in the content of ZnO, thus contributes to newenvironmental regulations.

Two mixtures are prepared from the mixture M7, which mixtures aredenoted M7−2 and M7+2 and in which the zinc oxide contents arerespectively −2 parts and +2 parts, with respect to the 5 parts presentin the mixture M7. The results obtained with use of metal oxides arepresented in the following Table 3:

TABLE 3 M0 M7 M7 − 2 M7 + 2 CR A base 194.5 194.5 194.5 194.5 Ekaland ®100 1 1 1 1 Paraffin 1 1 1 1 Mixland ® + ZnO 90 GA F100 5 5 3 7Mixland ® + ETU 80 GA F140 0.75 Ekaland ® bis-DMTD 0.75 0.75 0.5Mixland ® + DPG 80 GA F140 0.2 0.2 0.2 Rheometry on an MDR at 170° C. -according to Standard NFT 46-006 (or ISO 6502) C_(max)-C_(min) (dN · m)14.1 14.6 14 14.25 t_(s) 1 (min) 1.1 0.76 0.77 0.76 t_(c) 90 (min) 12.314.2 14 14.2 Scorch time on a Mooney viscometer at 125° C. according toStandard NFT 43-004 (or ISO 289-2) MS t3 9.7 6.1 5.9 6 MS t10 13.3 10.510.5 10.5 MS t18 24.3 14.8 15.2 14.9

Tests were also carried out in order to measure the influence of certainknown retardants used to increase the scorch time. The retardants testedhere are MBTS (mercaptobenzothiazole disulphide) and CTPI(N-cyclohexylthiophthalimide). The mixtures M11 and M12 were preparedand tested. The compositions of the mixtures M11 and M12, and theirperformances, with respect to the mixtures M0 and M7, are presented inthe following Table 4:

TABLE 4 M0 M7 M11 M12 CR A base 194.5 194.5 194.5 194.5 Ekaland ® 100 11 1 1 Paraffin 1 1 1 1 Mixland ® + ZnO 90 GA F100 5 5 5 5 Mixland ® +ETU 80 GA F140 0.75 — — — bis-DMTD powder (MLPC 0.75 0.75 0.75International) Mixland ® + SM300 80 GA F140 — — — 0.5 Mixland ® + DPG 80GA F140 — 0.2 0.2 0.2 Mixland ® + CTPI 80 GA F500 — — — 1 Mixland ® +MBTS 80 GA F140 — — 2 — Rheometry on an MDR at 170° C. - according toStandard NFT 46-006 (or ISO 6502) C_(max)-C_(min) (dN · m) 14.1 14.612.6 15.7 t_(s) 1 (min) 1.1 0.76 0.8 0.9 t_(c) 90 (min) 12.3 14.2 9 9.8Scorch time on a Mooney viscometer at 125° C. according to Standard NFT43-004 (or ISO 289-2) MS t3 9.7 6.1 8.5 9.1 MS t10 13.3 10.5 13.1 14.5MS t18 24.3 14.8 16.4 18.1

Example 2 Styrene/Butadiene Rubber (SBR) Vulcanization Test

As for Example 1 above, the mixing of components is carried out in a 2.5l Repiquet internal mixer at 50 revolutions/min with a fillingcoefficient of 1.4.

An “SBR base” is thus prepared, for which the natures and amounts ofmaterials introduced into the mixer are as follows (the parts areexpressed by weight):

Materials Parts SBR 1502 100 N220 (carbon black) 51 Exarol 25 oil 11.5Total 162.5

Two formulations S1 and S2 for vulcanization are prepared which have thecharacteristics presented in the following Table 5:

TABLE 5 S1 S2 SBR base 162.5 162.5 Mixland ® + ZnO 90 GA F100 5 5Stearic acid 3 3 Ekaland ® DPG c 0 0.5 bis-DMTD powder (MLPC Intl) 0.50.5 Mixland ® + SM300 80 GA F140 2 2 Rheometry on an MDR at 170° C. -according to Standard NFT 46-006 (or ISO 6502) ΔC (dN · m) 9.32 11.35t_(s) 1 (min) 2.16 1.72 t_(c) 90 (min) 23.9 16.3

The amine compounds (in this instance DPG) act synergistically with thebis-DMTD: the DPG promotes the release of sulphur, which increases thebridging degree and improves the kinetics of vulcanization.

Example 3 EPDM Vulcanization Test

As for the preceding examples, the mixing is carried out in a 2.5 lRepiquet internal mixer at 50 revolutions/min and a filling coefficientof 1.4.

The “EPDM base” used exhibits the following composition, in which theparts are expressed by weight:

Materials Parts EPDM Keltan ® 512x50 150 ZnO, active 4 Carbon black N550111 Liquid paraffin 17 Total 282

The results of tests carried out with 4 formulations denoted E1, E2, E3and E4 and prepared from the above EPDM base are presented in thefollowing Table 6:

TABLE 6 E1 E2 E3 E4 EPDM base 282 282 282 282 Stearic acid 2 2 2 2Ekaland ® ZBEC pd 1.4 1.4 1.4 1.4 Mixland ® + ZDTP 50 GA F500 3 3 3 3Mixland ® + DPG 80 GA F140 0.5 0 0.5 0.5 bis-DMTD powder (MLPC Intl) 00.5 0.5 1 Mixland ® + SM300 80 GA F140 2 2 2 2 Rheometry on an MDR at170° C. - according to Standard NFT 46-006 (or ISO 6502) ΔC (dN · m)10.8 10.6 10.9 11.3 t_(s) 1 (min) 0.36 0.43 0.39 0.43 t_(c) 90 (min)3.38 3.41 3.32 3.28

On comparing the formulations E1 and E2, it is found that bis-DMTD isequivalent in rheometry as replacement for DPG with a better scorchsafety. On comparing the formulations E2 and E3, a synergistic effect isobserved between bis-DMTD and DPG: a better bridging degree and areduced vulcanization time are obtained, while maintaining the scorchsafety. Finally, on comparing the results obtained with formulations E3and E4, it is noted that the increase in the amount of bis-DMTD furtheraccentuates the synergistic effect.

1-8. (canceled)
 9. A composition for the vulcanization of unsaturatedpolymers, comprising a mixture of bis(2,5-dimercapto-1,3,4-thiadiazole)and at least one organic base.
 10. The composition according to claim 9,wherein the at least one organic base is chosen from nitrogenous organicbases.
 11. The composition according to claim 10, wherein the at leastone organic base comprises a guanidine.
 12. The composition according toclaim 10, wherein the at least one organic base comprises a substitutedguanidine.
 13. The composition according to claim 12, wherein the atleast one organic base is a guanidine substituted by one or more arylgroups.
 14. The composition according to claim 12, wherein the at leastone organic base comprises diphenylguanidine.
 15. The compositionaccording to claim 9, wherein the bis(2,5-dimercapto-1,3,4-thiadiazole)to organic base molar ratio is between 1:99 and 99:1.
 16. Thecomposition according to claim 15, wherein thebis(2,5-dimercapto-1,3,4-thiadiazole) to organic base molar ratio isbetween 25:75 and 75:25.
 17. The composition according to claim 15,wherein the bis(2,5-dimercapto-1,3,4-thiadiazole) to organic base molarratio is approximately 50:50.
 18. A process for the vulcanization of anunsaturated polymer, comprising: mixing the unsaturated polymer with amixture of bis(2,5-dimercapto-1,3,4-thiadiazole) and at least oneorganic base, and vulcanizing the unsaturated polymer.
 19. The processaccording to claim 18, wherein mixing the unsaturated polymer with amixture of bis(2,5-dimercapto-1,3,4-thiadiazole) and at least oneorganic base further comprises mixing the unsaturated polymer withsulphur and/or one or more inorganic vulcanization agents.
 20. Theprocess according to claim 18, further comprising adding one or moreadditives chosen from lubricants, fillers, colourants, preservatives,antioxidants, heat stabilizers, UV stabilizers, and vulcanizationinhibitors or retardants.
 21. The process according to claim 18, whereinthe unsaturated polymer is chosen from natural, artificial or syntheticrubbers, poly(butadienes), styrene and butadiene copolymers (SBRs),acrylonitrile and butadiene copolymers (NBRs), ethylene/propylene/dienecopolymers (EPDMs), butyl rubbers, poly(styrene-butadiene styrene)copolymers (SBSs), halogenated polyalkadienes, and mixtures thereof. 22.The process according to claim 21, wherein the unsaturated polymercomprises a chlorinated polyalkadiene.
 23. The process according toclaim 21, wherein the unsaturated polymer is chosen from chioroprenerubbers or polychloroprenes, chlorinated natural rubbers, chlorinatedpolyolefins, chlorinated butyl rubbers, and mixtures thereof
 24. Theprocess according to claim 23, wherein the unsaturated polymer comprisespolychioroprene.